Special option H05 is obsolete. The detailed description of the option was, “Calibrated in Standards Lab for E.N.R. at 10 and 100 MHz and every GHz from 1 TO 26 GHz plus 26.5 GHz.” It appears the standard 346C is now calibrated using these same cardinal frequency points.

346C-H10:

Option H10 provides a National Physics Laboratory calibration that offers about 30% to 50% less ENR measurement uncertainty compared to a standard factory calibration. The data on the Noise Source data label will now be the NPL data (beginning Nov 2008). The diskette will also contain the NPL ENR data. The NPL ENR report is included with the shipment.